Process of and apparatus for separating air



Maly i3 i924.,

` H. N. DAVE@ ET L,

PROCESSV OF AND APPAHATS FR SEPARATUEG MCR Qiginal Fi`led-July 7. 1926 W ff @www w@ 7W um effect.

Patented May i3, i924.

man

PTENT @o HARVEY N. DAVIS AND ROBERT V. KLEINSCHMIDT, OF CAMBRIDGE, MASSACHUSETTS, ASSIGNORS TO RESEARCH CORPORATION, 0F NEW YORK, N. Y., A CORPORATION OF NEW YORK.

,PROCESS O'F AND APPARATUS FOR SEPARATING AIR.

Application led July 7, 1920, Serial No. 394,545. Renewed October 8, 1923.

To ZZ echo-m t may concern Be it known that we, HARVEY N. DAvis and Ronnfr V. KLEINSCHMIDT, citizens of the United States, residing at Cambridge, in the county of Middlesex and State of Massachusetts, have invented certain new and useful Improvements in Processes of and Apparatus for Separating Air, of which the following is a specification.

Our invention relates to the separation process commonly known as rectification, this being a process that is ordinarily carried on in a vertically elongated and enclosed space in which an ascending stream of vapor and a descending stream of liquid intermingle and interact. Such a pair of streams, together with the structure containing and controlling them may be called a rectification train. Into such a train pass, at one or more levels, streams of fluid of various compositions, and this invention relates more particularly to the use and manner of forming certain gaseous streams which it is highly advantageous to introduce into the lower part of such a rectification train.

In a copending application of Harvey N. Davis, Serial No. 394,544, filed July 7, 1920, reference is made to the advantages of either imparting heat to, or abstracting heat from, the contents of a rectification train at a plurality of well distributed levels, and'not merely at the top and bottom thereof, as has hitherto been practised. Reference is also made in the said co-pending application to the great and beneficial effectwhich the introduction of a plurality7 of liquid streams of appropriate compositions and magnitudes into the upper part of a rectification train has in reducing the amount of heat-transfer required for effective rectification at all levels, and it was stated that one or more gaseous streams of appropriate composition, introduced into the lower portion of a rectification train would have a similarly beneficial The present invention relates to the formation and use of gaseous streams of this kind. The object of ourinvention is then, to reduce the amount of heat-transfer necessary to secure effective rectification at all levels in a train, to improve the yield of such a train, and to decrease the cost of the product or products thereof, which may be either oxygen or nitrogen of any useful degree of purity or both.

For a full understanding of the invention, reference is had to the accompanying drawing, which represents one disposition of apparatus embodying the invention in combination with other appropriate elements.

It should be understood that this drawing does not represent the only disposition of apparatus in which our invention can be advantageously embodied, and that we do not limit ourselves to this or any otherv particular embodiment.

Aln the accompanying drawing, l represents a shell, still, or column containing the main rectification train. The shell l is equipped with a considerable number of trays 2 each with gas passing traps 3 and liquid passing traps 3a arranged in a Well known manner. Low pressure gaseous air enters the train through inlet 4, the said air having been precooled in a passage 5 in an auxiliary interchanger, which includes also the passages 6, 7 and 8, and in a main interchanger of any suitable construction (not shown). Through the inlet 7 a stream of largely or Wholly liquefied air enters the train. This stream is preferably obtained by cooling a stream of H. P. air, i. e., a stream of air under a pressure well above the critical pressure of air, in the main interchanger and subsequently in the passage 7 of the auxiliary interchanger in thermal contact with the cold nitrogen-rich productcoming from the top of the train and passing through the passage 6 of the auxiliary interchanger and then throttling the so cooled stream through the valve 7 into the still at a point intermediate the L. P. inlet 4 and the top of the train. By L. P. I designate a pressure which is substantially atmospheric pressure or not materially above atmospheric pressure.

A largely or Wholly liquid stream of nitro- -gen-rich fiuid enters the train through the valve 8 and inlet 8 at the top of the train. This stream, in this particular instance, is formed in a manner to be presently described.

The nitrogen-rich gaseous'product of the rectification process leaves the train through the pipe 9, coils 10 and pipe 1l and, as previously mentioned passes through the passage 6 of the auxiliary interchanger and subsequently through the main interchanger as fully described in the co-pendi'ng application referred to above.

Through the pipe 12 a stream of air enters the column under apressure less than its critical pressure. but materially higher than that in the main rectification train, which pressure l designate as T. P. This stream enters the upper part ot the chamber 13, which is surrounded by a pool 14 of oxygenrich liquid discharged from the lower end of the train, and is partly liquefied therein. The remaining gas passes through tubes 15 surrounded by increasingly colder liquids in the trays outside and further portions of it condense and drain backward. with rectification after the manner of Claude (see ll. S. Pat. 881,176). The nearly pure nitrogen gas remaining passes through the upper chamber 16 to the tubes 17 where it is largely or wholly liquefied, any unliquefied portions being drawn off through the pipe 18 and throttled into the stream of nitrogen product in the coils 10, or otherwise suitably disposed of. The nitrogen-rich liquid col-` lecting in the chamber 19 is withdrawn through pipe 20, further cooled in the passage 8 as indicated and throttled into the to a of the main rectification train.

]B v these means the liquid oxygen-rich product collecting in the bottom of the main train is evaporated and heat is imparted to the contents of the main train at a plurality of well distributed levels in the lower part thereof as set forth in the co-pending application referred to above.

The present invention is concerned primarily with the use that is made of the oxygen-rich liquid collecting in the chamber 13. In the present state of the art this is withdrawn through a. pipe 26, and throttled i tion train at a level 26) to which its composition is appropriate. namely at or somewhat above the level of inlet 4.

In the apparatus shown in the accompanying drawing, a part of this liquid is at once throttled through the valve 2.1 into a plurality of tubes 22 inside of and substantially concentric with the hereinbefore mentioned tubes 15. This liquid then partly or wholly re-evaporates in the tubes 22, meanwhile abstracting heat from the surrounding fluid in the tubes 15 and helping to condense the same. Finally the fluid in the tubes 22, now largely or wholly gaseous again, is discharged into the main rectification train at a level 23 to which the composition of its.

gaseous portion is appropriate.

Meanwhile another part of the oxygenrich liquid collecting in the chamber 13 is at once throttled through the valve 24 into a plurality of tubes 25 inside of and sub stantially concentric with the hereinbefore mentioned tubes 17, and is similarly largely or wholly re-evaporated, while helping to condense the fluid in the tubes 17. Finally this portion, now largely or wholly gaseous again, is also discharged into the main rectication train at the level 23.

The remainder, if any, of the oxygen-rich liquid collecting in the chamber 13 is passed through the above mentioned pipe 26 and valve 26a into the train at `the level 26", in. the usual way.

The chief advantage ol this process is that the level 23 lies materially below the lowest level (here the level l) to which any other available stream of fluid is appropriate. Under these conditions the heattransfer requirements of the main train between the levels 23 and 4 are very inuch reduced and may be made almost negligibly small. The quantity of liquid required for effective rectification at each and every level in the train above the level 23 is much smaller than in a similar train not embodying our invention, and in particular the quantity of nitrogen-rich liquid which must be fed to the upper most part of the train to secure any desired degree of effectiveness in the rectification in the upper part of' the train is materially reduced.

This process, whereby a liquid richer in oxygen than air is formed from air, separated Jfrom the remaining gaseous part ot the air` and largely or wholly re-evalporated, before being put into a rectification train. is the mos-t important feature of our inventio-n.

These advantages can be secured in still greater measure. if a plurality of' streams of liquid, of different compositions, but all richer in oxygen than air, are formed in any suitable manner7 as by successive partial liquefactions with or without rectification, of the stream 12, wholly or largely re-evaporated, and introduced into the main rectification train. each at the level to which the composition of its gaseous portion is appropriate. For the sake of simplicity we have not diagrammatically indicated this extended application of the invention. especially since it will be entirely comprehensible to persons familiar with the art.

Another advantage is afforded by the disposition of parts shown in the accompanying drawing. By proper manipulation of the two valves 21 and 2l the relative amounts of liquid passing into the two sets of tubes 22 and 25 can be adjusted at will. This gives a. useful measure oi control of the relative vigor of condensation in the two sets of tubes 15 and 17. For example, it the gas reaching the upper chamber 16 is not rich enough in nitrogen for satisfactory use in the upper part of the train, the valve 21 can be somewhat opened and the valve recaen 24 correspondingly closed, and more condensation will occur in the tubes 15 and less in the tubes 17 giving a urer nitrogen liquid in the chamber 19. lonversely, if more liquid is desired in the chamber 19, an opposite change in each valve will produce it. This disposition of parts whereby the liquid to be re-evaporated is divided into` two or more separately controllable I portions, whereby the relative rates at which heat is absorbed from different parts of the system is under control, also forms an important part of our invention.

Many modifications of the particular disposition of parts shown in the accompanying figure might be made without departing from the essence or scope of our invention. For example, the secondary interchanger, through which the streams 5, 6, 7 andv 8 pass, could be dispensed-with, and the heat-exchanging possibilities of the various streams concerned could be made use of in a variety of other ways, clearly indicated in the co-pendirg application referred to above, without departing from the essence or scope of our invention. These, and many other modifications of the particular disposition of parts which we have described herein, we hold ourselves free to make, as may be expedient, and, as hereinbefore mentioned, we claim the right to embody our`invention, or any of the elements thereof, fin other forms of rectification trains, within the limits of the appended claims.

It should be understood that in the foregoing our invention has been described in connection with Athe separation of air, merely, in order to furnish "a concrete example of its application and that it is, either in principle or in practice by no means limited thereto. The claims appended hereto have therefore not been limited to the separation of air explicitly but are broadly directed to the separation of any gaseous mixture which may lend itself to treatment by rectiicatio Inv the following formulation of the elements of our invention wer wish certain expressions, which are used as convenient abbreviations for much longer expressions, to be understood in each and every case to have the meanings assigned to them in this and the following paragraphs. The word rectification shall be understood to J refer to any process whereby a stream of served by fthese authorities for special classes of processes of this general type, and other expressions, such as clariicatioln dephlegmatiom continuous l'n'ogressive distillation, purification by selec-tive solubility,v`v` and so on, being used for other classes of such processes. It is desired that the word rectification in the following claims shall not be construed in any such restricted sense, but shall be understood to include any and all processes meeting the above very general definition, including processes in which material is added to or withdrawn from either or both streams in other ways than by transference between the two streams, and including processes in which heat is added to or withdrawn from either or both streams in other ways than by transference between the two streams.

It is also desired that the words train and rectification train be understood as referring either to the two interacting streams mentioned above` or to the enclosure, baffles, trays, and` so on used` to confine and control the said streams, as the context may indicate, but not to any other streams, or bodies of material, or to any pipes, passages, chambers,or other structural elements that may be contiguous to a rectification train or contained within the same structure or column that contains a rectification train.

Reference will frequently be made in the appended claims to a stream of material to be rectified or to a stream of fluid that enters or passes into a rectification train. It is desired that no part of the main stream of liquid appertaining to the rectification train itself, which is sometimes originated by a condenser at one end of the train, nor any part of the main stream of gas fappertaining to the rectification train itself, which is usually originated by the evaporation of a pool of liquid at the other end of the train, shall be confused with, or identified as any one of the streams explicitly mentioned in the following claims as entering or passing into a train or supplying a train with material to be rectified.

fn the appended claims a stream of fluid will sometimes be referred to as entering a rectification train at a. level to which the composition of the stream is appropriate. It is desired Athat this shall be understood to mean a region in the train where the gaseous stream of the train has substantially the same composition as that of the gaseous portion of the stream of fluid, -if the said stream is largely or wholly gaseous, and a region where the liquid stream of the train has substantially the same composition as that of the liquid portion of the stream of fluid, if the said stream is largely or wholly liquidi.

Finally, it is desired that whenever the phrase the less volatile constituent is used in the appended claims it shall have that one of the following meanings which is appropriate to the gaseous mixture to be separated. If the mixture is a true binary mixture, the phrase shall mean that one of the t\vo constituents which has the higher boiling temperature at the pressure at which the train is operated. If the mixture is air, the phrase shall mean oxygen. If the mixture is any other gaseous mixture which, like air, contains considerable quantities of two major constituents, and relatively much smaller quantities of other minor constituents, the phrase shall be understood to refer to the less volatile of the tivo major constituents. And in general the phrase shall be understood to refer to the constituent or constituents Which tend to concentrate at the warmer end of the rectification train. The phrase the more volatile constituent shall be interpreted in an analogous and complementary Way.

We claim 1. In a process of separating a gaseous mixture by rectification into portions of different compositions, the steps which consist in forming a largely or wholly gaseous stream richer in the less volatile constituent than the mixture to be separated, and passing the said stream into the rectification train .at a point intermediate the ends thereof.

2. In a process of separating a gaseous mixture by rectification into portions of different compositions, the steps Which consist in forming, in thermal but not direct contact with portions of a rectification train, a largely or Wholly gaseous stream richer in the less volatile constituent than the mixture to be separated, and then passing the said stream into the train.

3. In a process of separating a gaseous mixture by rectification into portions of different compositions, the step which consists in passing into a rectification train a largely or Wholly gaseous stream richer in the less volatile constituent than the original mixture.

4. In a process of separating a gaseous mixture by rectification into'portions of different compositions, the steps Which consist in passing into a rectification train ay plurality of largely or Wholly gaseous streams of different compositions.

5. In a process of separating a gaseous mixture by rectification into portions of different compositions, the steps which consist in passing into a rectification train one or more not Wholly liquid streams, the gaseous portion of at least one of which is materially richer in the less volatile constituent than the original mixture. i

6. In a process of separating a gaseous mixture by rectification into portions of dif- Legami ferent compositions, the steps which consist in passing into a rectification train three or more streams of different compositons, at least one of Which is largely or Wholly liquid, and at least two of which are largely or Wholly gaseous.

7. In a process of separating a gaseous mixture by rectification into portions of different compositions, the steps which consist in passing into a rectification train a plurality of largely or wholly gaseous streams, at least one of which is richer in the less volatile constituent than the original mixture, and one or more streams chiefly or Wholly in the liquid state.

8. In a process of separating a gaseous mixture by rectification into portions of different compositions, the steps which consist in passing into a rectification train a cooled but unliquefied stream of the original niixture, introduced at a level to which its composition is appropriate, and one or more largely or Wholly gaseous streams richer in the less volatile constituent than the original mixture, each such stream being introduced at a level Warmer than the level at which the above mentioned unliquefied stream enters, but cooler than the Warmer end of the train.

9. In a process of separating a gaseous mixture by rectification into portions of di fferent compositions, the steps which consist in passing into a rectification train a plurality of streams, one of which is largely or Wholly liquid and rich in the more volatile constituent of the mixture, and another of Which is largely or Wholly gaseous, and is richer in the less volatile constituent than the original mixture.

u 10. In a process of separating a gaseous mixture by rectification into portions of different compositions, the steps which consist in passing into a rectification train three or more streams of different compositions, at least one of which is largely or Wholly liquid, at least one vof which is gaseous and has the composition of the original mixture, and at least one of which is largely or Wholly gaseous and is richer in the less volatile constituent than the original mixture.

11. In a process of separating a gaseous mixture by rectification into portions of different compositions, the steps which consist in passing into a rectification train a plurality of largely or Wholly gaseous streams of different compositions and a plu ality of largely or Wholly liquid. streams of different compositions.

12. In a process of separating a gaseous mixture by rectification into portions of different compositions, the steps which consist in passing into a rectification train four or more streams, one of which is largely or Wholly liquid and rich in the more volatile constituent, one of which is largely or Wholmesma Umixture by rectification into portions of dif- :ferent compositions, the steps which consist f in partly liquefyng astream of themixture to be separatedVremoving at least part ofy the liquid thus formed from the remainder 15 of the stream, freevaporating lthe removed liquid, and passing `the resulting gas into the rectification train.

14. ln a process of separating a gaseous mixture by rectification into portions of different compositions, the steps which consist in partly liquefying under-pressure a stream of ,the mixture to be separated, removing at least part of the liquid thus formed fromi the remainder of the stream, reevaporating a substantial-portion of ,the removed liquid resulting stream into the rectification train."

partly by throttling andpartly by ,causing heat to be transferred to it, and passing the 15. ln a process of separating a gaseous 3 mixture by rectification into portions ofdif- -ferent compositions,- the steps which consist in partly liquefying a stream of the mixture to be separa-ted with concurrent rectification, removing at least part of the liquid thus formed from the remainder of the stream, reevaporating substantially the Whole of the liquid thusxremovedand passing the resulting stream into the main rectification train. .i "f

16. In a process of separating a gaseous mixture by rectification into portions of different compositions, the steps which consist in forming, in thermal but not direct contact with a partrof the main rectification train, a liquid richer in the less volatile constituent `rthan .the mixture, subjecting the said liquid to substantially complete reevap-' oration, and then subjecting the reformed gas to rectification in: another part xof the main train. j

.17. liny a process of separating a gaseous mixture by rectification into portions ofdifferent compositions, the steps which consist in subjecting, in thermal but not direct contact witha part of the main rectification train, a stream of the mixture to partial liquefaction with secondary rectification to form a liquid richer in the less volatile coni stituent than the mixture, subjecting the said liquid to substantially complete reevaporation, and then subjecting the resultiiig gasto rectification in'another part of th main train. l f

18. In a process of separating a gaseous mixture by rectification into portions of different compositions, thesteps which consist .y in progressively condensing out of a stream' of the mixture to be separated, a plurality of liquid portions of diHerent compositions,

at least one of which is richer in the less `volatile constituent than the original mixture, subjecting a liquidportion rich in the less volatile constituent to substantially complete reevaporation, and passing the reformed gas, and the other liquid or liquids into dierentparts of a'rectification train.

19. In a processof separating a gaseous mixture by rectification into portions of different compositions, the steps Ywhich consist in bringing a stream ofthe mixture, under a pressure higher than that of the main rectification train, but lower than the critbut notldirect contact with portions of"the main train, sothat a part of the mixture is liquefied, separating at least partk of the liquid thus formed from the remaining portion ofthe fiuid thus treated, reducing the pressureof'the separated liquid, then bringl ing the resulting stream in thermal but not direct contact with fluids warmer than itself, thus causing the remainingiliquid to largely or wholly reevaporate, and then passingdthisA reformed gas into the main rectification train. i y

20. Apparatus for separating a gaseous yical pressure of the mixture, into thermal mixture into portions ofdifferent composi' l ltions, comprisipg a main rectification train, means for forming alargely or wholly gascous stream richer in the less volatile con stituent than the mixture, and means for introducing the said stream into the train at a point intermediate the ends thereof.

.21. Apparatus for separating a'gaseous mixture into portions of different compositions, comprising a main rectification train,

means adjacent to the Warnier part ofv tle .train for forming, in thermal but not direct contact with the contents of a portion of the train, a largely or wholly gaseous stream ripher in the lessvolatile constituent than the original Jmixture, and means for passing the .said stream into the train.

22. Apparatus for separating a gaseous mixture into portions of different compositions, comprising a main rectification train, means for forming' a largely or wholly liquid stream rich vin the more volatile constituent and for introducing the said stream into the train at a level at or near its colder end, means for forming a 'largely or Wholly gaseous stream richer in the lessV Volatile'constituent than the 5 original mixture, and means for introducing the said stream into the train at a level intermediate the ends thereof.

23. Apparatus for separatingv a gaseous l l i J the trainjat a level intermediate` the ends thereof, means for forming a largely or.

wholly gaseous stream .richer in the less-1 volatile constituent than the original mixture, and means 1for introducing the said stream into the train ata levelintermediate the entry level of the original mixture and the warmer end of the train.

24. Apparatus for separating a gaseous mixture into portions of different compof sitions, comprising a main rectification train, means for Jforming a largely or Wholly liquid `stream rich in the more .volatile constituentl and for introducing it into `the train at a level at or near the colder end of the. train means -for introducing a previously cooled gaseous stream of the original mixture into the train at a somewhat warmer level, means `for forming a largely or 'wholly gaseous.

streamricher in the less yolatile constituent than the original mixture, and means for introducing the said streaminto the train' at a level intermediate the entryilevel of the original mixture and the warmer end of the train.

, 25. Apparatus `ifor separating a gaseous mixture into portions of difierent compositions, comprising a" main rectification train, means for forming a largely or Wholly liquid stream `havimg as a Whole the composition of the original mixture and for introducing the said stream into the train at a level inrtermediate the ends thereof, means for formy nal mixture, and means .for introducing the ing a largely orrwholly gaseous stream richer in the less volatile constituent than the origisaid stream intov the train at a level inten-r mediate the entry level of the liquid stream and the warmer end of the train.y

26. Apparatus for separating a gaseous mixture into portions of dfierent composi tion, comprising a main rectification train, means in thermal lout not direct contact `with part of the train near its *Warmer endl for forming a largely or Wholly gaseous stream richer in the less `volatile constituent hut materially less rich than the product leaving the train at its Warmer end,'ineans for introducing thesaid stream into the train '/aty a level to which its composition is appropriate, means tor vintroducing into the train at a relatively colder level a previously cooledv gaseous stream of the original mixture, and

meansy ior introducing into the train at a still colder level,va stream oi largely' or Wholly liquefied mixture.

g?. Ap aratus tor separating a: gaseous C@ mixture into portions of different composiassenti having as a whole the composition of the original mixture and yfor introducing this second stream into the train at a somewhat warmer level than that at which the first stream is introduced, means'fr, forming, a largely or Wholly gaseous stream richer in the lessVOlati-le constituent than the original mixture, and means for introducing 'this third stream into the train at a level intermediate the entry level of the second lstream and the warmer' end-of .the train. w'

28. Apparatus for separating agaseous mixture into portions of dierent compositions, comprising-a main rectification train, means for forming a largely or Wholly liquid stream richin the more volatile constituent and for introducing the said stream into the train at .aylevel at or near its colder end, nieansfor formino' a largely or WhollyliquidJ stream having as "a ,whole the composition of-tlie`original mixture and for introducing this second stream into the train at a sce-MQh y what Warmer level, means tor introducing a previously cooled gaseous, stream of the original mixture into thetrain at a Vstill 'Warmer level means for forming a ylargely or Wholly gaseous stream richer inthe less volatile ,constituent than the original mix@ having forms, temperatures and compositionsappropriate to dierent' Well distributed levels in the train, at least. one of ,these streams losing largely or Wholly gaseous and richer inthe less 'volatile constituent than the original ,mixture hut materially less rich than the product leaving the train at its Warmerend, and 'means tor .introducing theY said streams into-the train at their appropriate levels. 1 30. Apparatus ier separating a gaseous mixture into portions ont different compositions, comprising a main rectification train,y means for suhjectin a stream ci the mixtureto partial lique' action, means for separating at least art oi the resulting liquid from the remainder oi the stream, 'means for largely or Wholly] reevaporating the separated liquid, means orintroducing the l resulting stream into the main rectification train, and means lor passing the remainder oil-the original stream into the train.

3l. Apparatus Vfor?separating a gaseous mixture into portions ot diii'erent compositions, comprising a main rectification train, means tor subjecting a stream oi the mixture to ,partial liqueiaction with rectification, means :tor seoarating at least part of the resulting liquid Jfrom the remainder of ist lil() liquefied, means for separating at least part of the liquid thus formed `from the remainder of the stream thus treated, means for reducing the pressure of ther separated liquid, meansY for putting the resultingA stream in thermal but not, direct contact y -with fluids warmer than itself, whereby substan'tially all the remaining liquid is reevapstream into the main rectificationtrain, and' orated, means for introducing the resulting means for passing the remainder of the original stream into the train.

33. Apparatus for separating a gaseous mixture into portions .of diiierent composi tions, comprising a column containing a main rectification train, means i-n the lower or warmer part of the said column defining archamber, a plurallty of tubes extending upwardly' from said chamber in thermal chamber and tubes and collects in the lower s part-of the chamber, means for admitting liquid from the lower part of thechamber Kto the said pipes, means orcontrolling the said admission and for reducing the Iressure of the liquid during said admission, an outlet from the upper ends of the tubes, and means connecting the upper ends of the pipes withdthe main rectification train.

84. Apparatus for separating a gaseous mixture intofportions of dii'erent compositions, comprilsing a column' containing a main rectification train, means in the lower part of the said column defining two sepa rate chambers, tubes 'extending upwardly from each of the said chambers in thermal butnotdirect contact? with increasingly colder regions in the train, means at the upper ends of the tubes definingapassage betubes from s the other chamber, an Aoutlet from the upper part of said passage, means for introducing vinto the upper part of the first of said chambers astream eo tween the tubes from one chamber and the Y 'I ot previously cooled gaseous mixture unf der a kpressure higher than that in the main train but lower than the critical pressure ofthe mixture, whereby a part of the said stream is liquefied in the firstchamber and-the tubes extending therefrom and collects in the lower part of the first chamber, an outlet from the bottom of the second of the said chambers, pipes extending upwardly from the first chamber through the tubes connecting therewith and through the passageri'nto the main train, other pipes' eX- tending upwardly from the second chamber through the tubes connecting therewith and through ,the passage into 'the main train, means for admitting liquid from the lower part of the 'first chamber into the lowerends of each of the said'sets of pipes and-means for controlling the said admissions to the two sets of pipes independently and for reducing the pressure of the liquid during said admissions.

In testimony whereof, we aiiix our signatures. 7

'HARVEY u. Davis. ROBERT V. KiiEiNsoHMin'r. 

